1. Technical Field
The present invention relates to a droplet discharging head and a droplet discharging device both of which discharge ink or liquid and a method for manufacturing the same, and more particularly to a compact stable droplet discharging head and a device without having electrical failures and a method for manufacturing the same.
2. Related Art
As a device for discharging a droplet, an inkjet head built in an inkjet recording device is known. Generally, the inkjet head is provided with a nozzle substrate having a plurality of nozzle holes for discharging an ink droplet, and a cavity substrate that has a discharge chamber bonded to the nozzle substrate so as to communicate with the nozzle hole and an ink flow path such as a reservoir. The inkjet head discharges an ink droplet from a selected nozzle hole by applying pressure to the discharge chamber. Examples of methods for discharging an ink droplet include an electrostatic driving method using electrostatic force, a piezoelectric method using piezoelectric elements, and a bubble jet (registered trade mark) method using heater elements.
The inkjet head employing the electrostatic driving method is provided with a cavity substrate in which the bottom of a discharge chamber serves as a vibration plate and an electrode substrate that is bonded to the cavity substrate and has an individual electrode facing the vibration plate with a predetermined gap. For discharging an ink droplet, an applied driving voltage charges the individual electrode positively and the vibration plate negatively. The applied voltage produces electrostatic force to elastically deform the vibration plate toward the individual electrode. Upon turning off the driving voltage, the vibration plate is restored. This restoring movement rapidly increases the pressure inside the discharge chamber, thereby discharging a portion of ink in the discharge chamber from the nozzle hole as an ink droplet.
In recent years, in the inkjet head employing the electrostatic driving method, highly densified and multi-rowed nozzles have been developed for high-speed and multi-color printing high-resolution images. Along with this development, the number of nozzles and discharge chambers per row has increased and the length of nozzle rows has been elongated. As a result, the number of actuators inside the inkjet head has been more and more increased. On the other hand, a structure has been proposed in which an IC for controlling actuators is built in the inkjet head for downsizing the inkjet head.
, JP-A-2001-63072 discloses an inkjet head as one of such examples (page 5 and FIG. 1.) The inkjet head includes single or multiple nozzles discharging an ink droplet, a discharge chamber communicating with each nozzle hole, a vibration plate serving as at least one wall of the discharge chamber, driving means for causing the vibration plate to be deformed and an individual electrode by which the driving means deforms the vibration plate with electrostatic force. In addition, a first substrate in which the vibration plate is formed is a single-crystalline substrate and a second substrate in which the individual electrode is formed is a glass substrate. A method for manufacturing the inkjet head includes the following steps. As means for maintaining a gap between the vibration plate and the individual electrode, either a gap spacer made of a SiO2 film is formed to the first substrate or a recess is formed to the second substrate. Next, the vibration plate and the individual electrode are faced and anodic bonded. Then, the vibration plate is etched to a determined thickness. This etching step includes two steps: a region (a contact area) of the first substrate is simultaneously etched to the same thickness as that of the vibration plate when the vibration plate is etched where the region is larger than the area, facing the region, of a terminal part for supplying voltage to the individual electrode (external electrode for the individual electrode) on the second substrate; and then silicon remaining in the contact area is dry etched to form a thorough hole. Additionally, an etching cover film is formed on the external electrode for the individual electrode facing the contact area. The etching cover film withstands silicon dry etching and can be selectively removed with respect to the electrode.
In the disclosed inkjet head, the insulation film having high insulation property and sufficient etching resistance is formed on the individual electrode as the etching cover film to prevent the electrode from being damaged by etching the through hole and leak current between electrodes. The inkjet head, however, needs to form the etching cover film on the substrate on which the individual electrode has been wired, to perform a patterning and to remove the used etching cover film. As a result, the number of manufacturing steps increases. In addition, only limited materials are usable. That is, some materials cannot be processed.
As a countermeasure, the insulation film may be formed after opening a portion of the silicon substrate by dry etching. However, this method also needs to remove the formed insulation film, so that a new problem arises. That is, when removing the formed insulation film, it is very difficult to remove the insulation film only formed on a part corresponding to a driver IC mount area and an FPC mount area while the insulation film remains that is formed on a wall face of the opening of the silicon substrate.